The size of a marble display box suitable for carrying on business trips depends on various factors, including the quantity and size of marble samples you need to transport, as well as the mode of transportation and personal preferences. 

    Generally, for business trips where you need to showcase a range of marble samples to clients or partners, a compact and lightweight display box that can hold a selection of smaller samples would be ideal. A size around 12 inches (30 cm) in length, 8 inches (20 cm) in width, and 4 inches (10 cm) in height could be suitable for carrying on business trips, as it is portable yet spacious enough to accommodate several samples while remaining manageable during travel. 

    Additionally, consider features like sturdy construction, secure closures, and protective padding to ensure the safety of the marble samples during transit.